1. Field of the Invention
The present invention relates to a liquid ejection head and a method of manufacturing a liquid ejection head, and more particularly, to a liquid ejection head having a laminated structure in which a plurality of plate members are arranged to overlap each other.
2. Description of the Related Art
There are print heads (liquid ejection heads) having a structure in which a plurality of plate members overlap each other, a pressure change being generated in ink accommodated in pressure chambers by means of the displacement of piezoelectric elements disposed on a diaphragm constituting at least one wall face of the pressure chambers, and ink droplets thereby being ejected from nozzles connected to the pressure chambers.
As a method for manufacturing a print head having a laminated structure of this kind, for example, there is a method in which recess sections or through holes corresponding to pressure chambers are processed in a plurality of ceramic green sheets, the green sheets are arranged to overlap each other, piezoelectric bodies are printed as paste onto the green sheet corresponding to the diaphragm, and the structure is then calcined together. Paste printing allows the formation of a highly dense pressurized film, which has high pressure resistance, but unless it is calcined at 900° C. or above, satisfactory properties are not obtained in the film. On the other hand, if an aerosol deposition (AD) method is used, then it is possible to obtain piezoelectric bodies having satisfactory properties, by annealing at a temperature of around 600° C. However, with the aerosol deposition method, it is difficult to form piezoelectric body films on a green sheet.
A method using aerosol deposition is known in which, as shown in FIG. 9, a plurality of ceramic green sheets are manufactured (step S110), fine recess sections or through holes corresponding to the pressure chambers are processed in the plurality of green sheets (step S112), the green sheets are arranged to overlap each other (step S114) and calcined (step S116), piezoelectric body films are formed by the aerosol deposition method on the ceramic sheet corresponding to the diaphragm (step S118), and finally, the piezoelectric bodies are annealed (step S120). The pressure chambers are formed at the completion of step S116.
However, in this method, there is a risk that the dimensional accuracy of the ink flow channels will decline due to lamination errors in the step of arranging the green sheets in step S114. Moreover, there is also a risk of a decline in the dimensional accuracy of the recess sections or through holes formed in the calcined sheets (ceramic sheets) obtained by calcining the green sheets in step S116, due to thermal contraction of the sheets. Furthermore, since the pressure chambers are formed at the completion of step S116, there is a problem in that it is difficult to form piezoelectric bodies by the aerosol deposition method onto the calcined green sheet corresponding to the diaphragm, which constitutes a wall of the pressure chambers.
Japanese Patent Application Publication No. 8-230181 discloses a piezoelectric unit in which titanium film and platinum film are formed by sputtering onto a silicon substrate, and a lead zirconate titanate (PZT) film of a prescribed shape is formed thereon by the aerosol deposition method and then calcined, whereupon gold electrodes are applied on top of the PZT film.
In this method, the piezoelectric units are bonded to the diaphragm or a cavity plate by means of adhesive; however, there is no discussion of the actual bonding method. When bonding together a plurality of plate members in order to manufacture a print head, it is common to use an epoxy type resin as the adhesive, but depending on the pressurization conditions and the temperature during bonding, the bonding strength may be insufficient, and the piezoelectric units are liable to peel away from the diaphragm or cavity plate, and hence reliability is low.
Japanese Patent Application Publication No. 2003-142750 discloses a method of manufacturing piezoelectric bodies patterned in an array configuration, by applying a silica (SiO2) film to the whole surface of a stainless steel substrate by sputtering, layering an electrode-forming Ti film or Pt film over the whole surface thereof, forming a prescribed resist pattern thereon by photolithography, forming a PZT film (piezoelectric body film) on the substrate so as to cover the resist pattern by the aerosol deposition method, creating a further electrode-forming Ti film or Pt film thereon by sputtering, and finally, removing the resist by a lift-off process.
In this method, however, a resist pattern is formed, a PZT film is then formed, the PZT film on the resist is then removed with the resist in a lift-off step, the structure is then annealed, and holes are then opened in the rear surface of the stainless steel substrate by selective etching in order to form pressure chambers. Therefore, complicated steps are involved, and the process is time-consuming and costly.
Japanese Patent Application Publication No. 2003-63017 discloses a method (glass bonding method), in which thin glass films are formed on the surfaces of plate members which each have ink flow apertures (groove hole sections) that form a single ink flow channel when the plate members overlap each other, and the plate members are then arranged to overlap each other in such a manner that their respective ink flow apertures are partially coinciding, whereupon they are pressurized and heat-treated, thereby softening the thin glass films between the plate members and thus bonding the plate members together.
In this method, ferrite type stainless steel SUS 446, or an iron-nickel-cobalt alloy containing 29% of nickel and 17% of cobalt (product name: Cobal), or the like, is used as the material of the plate members on which thin glass substrates are formed, and the heating temperature during bonding of the plate members is 400° C. or below. Therefore, a problem arises in that the step requiring annealing at 600° C. or above, such as the formation of the piezoelectric body films by the aerosol deposition method, and the step of glass bonding, cannot be carried out simultaneously, and therefore, the overall process becomes complicated. In particular, if the plate members are made of ceramic green sheets, then as described previously, the green sheets undergo thermal contraction during calcining, and the dimensional accuracy of the recess sections or through holes formed in the green sheets declines. In particular, there is a problem in that, if the dimensional accuracy of the pressure chambers falls and variations arise in the volumes of the pressure chambers, due to thermal contraction of the ceramic, then this will affect ejection performance, such as the ejection volume and ejection speed, and the like, of the ink droplets ejected from the nozzles, thus leading to a decline in print quality.